1. Field of the Invention
The present invention relates to an analytical cell suitable for use, e.g., in an electrode reaction analysis in an analytical equipment.
2. Description of the Related Art
As is well known, in an electric cell, a negative electrode active material and a positive electrode active material undergo electrode reactions in the charge-discharge process. In recent years, the electrode reactions have been analyzed during the charge-discharge process using analytical equipment. For example, an analytical cell that can be observed by a transmission electron microscope (TEM) has been proposed in In-situ Electron Microscopy of Electrical Energy Storage Materials [online], 2014, Retrieved on Jan. 30, 2014 from the Internet <URL: http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review—2011/electrochemical_storage/es095_unocic—2011_o.pdf>.
This analytical cell contains a pair of silicon substrates, each of which has a rectangular observation window having a size of about 50 μm×100 μm. The silicon substrates are stacked at a predetermined distance from each other to form an overlapping portion in such a manner that the observation windows face each other. A negative electrode active material containing a highly oriented graphite and a positive electrode active material containing LiCoO2 are located between the observation windows.
Specifically, on one of the silicon substrates, a negative electrode collector and a positive electrode collector are disposed outside of the observation window. The negative electrode collector extends from the inside of the overlapping portion and is exposed to the outside. The negative electrode active material and the positive electrode active material are formed in a plate shape by an ion beam deposition method, and extend from the negative electrode collector and the positive electrode collector to the inside of the observation window, respectively, in the overlapping portion. Incidentally, the negative electrode active material and the positive electrode active material having the plate shape are each extracted from a bulk body using a focused ion beam (FIB). Thus, the negative electrode active material and the positive electrode active material are electrically connected to the negative electrode collector and the positive electrode collector, respectively. Therefore, the negative electrode active material and the positive electrode active material can be electrically connected to an external circuit such as a charge-discharge tester by the exposed portions of the negative electrode collector and the positive electrode collector formed outside of the overlapping portion.
The electrode reactions and the like of the negative electrode active material and the positive electrode active material can be analyzed by observing the analytical cell using the transmission electron microscope (TEM). Specifically, first, the analytical cell is placed in an end of a TEM holder having a passage for introducing an electrolytic solution to the overlapping portion. Then, the electrolytic solution is introduced from the passage of the TEM holder into the overlapping portion, and the exposed portions of the negative electrode collector and the positive electrode collector formed outside of the overlapping portion are each connected to a charge-discharge tester or the like, whereby the negative electrode active material and the positive electrode active material undergo the electrode reactions. The TEM observation is carried out while transmitting an electron beam through the observation window to analyze the electrode reactions of the negative electrode active material and the positive electrode active material.